The main topic of the passage is（）

单项选择题It is implied in the passage that （）

A．governments and companies had different opinions about the safety of products
B．governments paid little attention to the safety of products
C．government officials often did not listen to scientists
D．in the past no safety laws were introduced by governments

单项选择题Some years ago safety rules （）

A．were put forward due to scientists' recommendations
B．came into being as a result of the workers' demand
C．were introduced because quite a number of people were killed or seriously injured
D．were effective enough to protect workers and customers